TripleFormatter.cpp

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/*
 * This file is part of KnowRob, please consult
 * https://github.com/knowrob/knowrob for license details.
 */
 
#include <filesystem>
#include <fstream>
#include "knowrob/semweb/TripleFormatter.h"
#include "knowrob/semweb/PrefixRegistry.h"
#include "knowrob/Logger.h"
 
bool knowrob::semweb::TripleFormatter::exportTo(
    const ExportedTriples &triples,
    const std::string &filename,
    TripleFormat format) {
    switch (format) {
        case TripleFormat::RDF_XML:
            return exportRDF_XML(triples, filename);
        case TripleFormat::TURTLE:
            return exportTurtle(triples, filename);
        default:
            // Unsupported format
            KB_WARN("Unsupported format: {}", tripleFormatToString(format));
            return false;
    }
}
 
static void ensureDirectoryExists(const std::string &filename) {
    std::filesystem::path path(filename);
    if (path.has_parent_path()) {
        std::filesystem::create_directories(path.parent_path());
    }
}
 
bool knowrob::semweb::TripleFormatter::exportRDF_XML(
    const ExportedTriples &triples,
    const std::string &filename) {
    ensureDirectoryExists(filename);
    // open file for writing, overwrite if it exists
    std::ofstream file(filename);
    if (!file.is_open()) {
        KB_WARN("Could not open file {} for writing.", filename);
        return false;
    }
    // write RDF/XML header
    file << "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
    file << "<rdf:RDF xmlns:rdf=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\"\n";
    file << "         xmlns:rdfs=\"http://www.w3.org/2000/01/rdf-schema#\"\n";
    file << "         xmlns:owl=\"http://www.w3.org/2002/07/owl#\"\n";
    // iterate over known namespaces
    for (const auto &[uri, prefix]: PrefixRegistry::get()) {
        file << "         xmlns:" << prefix << "=\"" << uri << "\"\n";
    }
    file << ">\n";
 
    // write triples
    for (const auto &[subject,exportedTriples]: triples) {
        file << "  <rdf:Description rdf:about=\"" << subject << "\">\n";
        for (auto &triple : exportedTriples) {
            auto property = triple->predicate();
            auto valueString = triple->createStringValue();
            auto valueType = triple->xsdType();
            if (triple->isXSDLiteral()) {
                // XSD property assertion
                file << "    <" << property << " rdf:datatype=\"" << xsdTypeToIRI(valueType.value()) << "\">";
                file << valueString << "</" << property << ">\n";
            } else if (triple->isObjectIRI()) {
                // object property assertion
                file << "    <" << property << " rdf:resource=\"" << valueString << "\"/>\n";
            } else {
                // untyped literal
                file << "    <" << property << ">" << valueString << "</" << property << ">\n";
            }
        }
        file << "  </rdf:Description>\n";
    }
    // write RDF/XML footer
    file << "</rdf:RDF>\n";
    file.close();
    return true;
}
 
bool knowrob::semweb::TripleFormatter::exportTurtle(
    const ExportedTriples &triples,
    const std::string &filename) {
    ensureDirectoryExists(filename);
    // open file for writing, overwrite if it exists
    std::ofstream file(filename);
    if (!file.is_open()) {
        KB_WARN("Could not open file {} for writing.", filename);
        return false;
    }
    // write Turtle header
    file << "@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .\n";
    file << "@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .\n";
    file << "@prefix owl: <http://www.w3.org/2002/07/owl#> .\n";
    // iterate over known namespaces
    for (const auto &[uri, prefix]: PrefixRegistry::get()) {
        file << "@prefix " << prefix << ": <" << uri << "> .\n";
    }
    // write triples
    for (const auto &[subject, exportedTriples]: triples) {
        file << subject << " ";
        bool isFirst = true;
        for (auto &triple : exportedTriples) {
            auto property = triple->predicate();
            auto valueString = triple->createStringValue();
            auto valueType = triple->xsdType();
            if (!isFirst) {
                file << ";\n  ";
            }
            isFirst = false;
            if (triple->isXSDLiteral()) {
                // XSD property assertion
                file << property << " \"" << valueString << "\"^^<" << xsdTypeToIRI(valueType.value()) << "> ";
            } else if (triple->isObjectIRI()) {
                // object property assertion
                file << property << " <" << valueString << "> ";
            } else {
                // untyped literal
                file << property << " \"" << valueString << "\" ";
            }
        }
        file << ".\n"; // end of the subject block
    }
    // write Turtle footer
    file << "\n";
    file.close();
    return true;
}